Abstract:

Alien plants cost the New Zealand economy over $1 billon per annum in lost revenue and control measures, and can modify native plant communities to the detriment of endemic biodiversity. Hieracium lepidulum has invaded several regions of New Zealand and is found in high densities among the hills in Central Otago. The roles of microbes are increasingly included in theoretical models of plant invasion, and this study investigates the diversity and spatial structure of a group of ubiquitous organisms, the arbuscular mycorrhizal fungi (AMF), growing in symbiosis with Hieracium lepidulum.

Three AMF-specific molecular primer sets were tested to determine their relative sensitivity and specificity for detecting AMF in cultures established from field collected propagules. The optimal primer set was then used to characterise the AMF community associated with H. lepidulum in modified subalpine grassland. The fungi from 30 plant individuals within a 1.8 × 1.8 m plot were characterised using restriction fragment length polymorphism (RFLP) analysis and cloning. AMF communities colonising individual plants were found to be diverse, uncorrelated with root biomass, and possess significant phylogenetic structure. Nine phylogenetically distinct taxa were defined, with no plant individual possessing more than seven taxa, despite one AMF taxon comprising over 67% of total abundances. Spatial analysis found evidence of significant positive spatial autocorrelation in the identities of AMF colonising neighbouring H. lepidulum up to 0.5 m. Spatial clustering was also detected in the distributions of H. lepidulum individuals at similar scales, potentially indicating common mechanisms structuring both host and symbiont distributions.

Phylogenetic analysis of the sequence data found evidence that the detected AMF taxa were potentially endemic and widespread generalists, indicating that the success of H.lepidulum as an invader is not likely to be the result of facilitation by coinvasive AMF.